The present invention relates to improvements in gate valve assemblies and, more particularly, to an improvement in the operating apparatus for a gate valve of the type having an operating stem which extends upwardly through the valve housing and through a support yoke for cooperation, typically, with a hand wheel where rotation of the hand wheel will be translated into rectilinear motion of the valve stem whereby the valve element will be moved between opened and closed positions depending on the direction of rotation of the hand wheel.
In the manufacture of fluid control systems, such as municipal water systems, fire protection systems including sprinklers as well as irrigation systems, the various flow control elements such as gate valves and the like must often reliably operate after long periods of non-use. For example, in municipal water systems, many of the flow control devices such as gate valves will normally remain open and need only be operated between their normally opened and their closed positions upon the occurrence of a leak in the system requiring the shut down of flow through the system to permit repair work to commence. Similarly, in fire protection systems such as building sprinkler apparatus, the various valve systems employed will only be put in operation during or after an emergency which is usually an infrequent event. In other fluid distribution systems, operation of large gate valves, for example, would normally only be effected during the periodic maintenance of the system.
As a consequence, in such systems, it is essential that the valve operating mechanisms be so constructed as to assure reliable operation when needed. In the case of fire protection systems it is also necessary that the systems be easily placed into service despite the long periods of non-use that the systems may experience.
In connection with large scale flow control devices such as gate valves that are stem actuated to move a valve element between an open and close position relative to a flow passage, the critical connections of the valve stem to a drive mechanism such as a hand wheel have employed a number of different assemblies for transmitting the rotary power of the hand wheel to the operating stem of the valve member itself. Some of these require frequent lubrication to assure smooth operation while others have been relatively difficult and expensive to assemble thus contributing to their high cost in even a mass production assembly line. In other arrangements, particularly those where the valve apparatus will lie idle for long periods of time, relatively complicated safety mechanisms have been employed to minimize the possibility of damage to the valve stem or valve element where resistance to movement is encountered when an attempt is made to operate the valve. It sometimes occurs that such safety mechanisms prevent operation of the valve by disengaging the stem raising mechanism so that little or no damage would result to the valve elements when torque is applied to the operating device. This is a particularly troublesome disadvantage in the use of valves employed in fire protection systems.